Effect of cassava starch gel, fish gel and mixed gels and thermal treatment on structure development and various quality parameters in microwave vacuum-dried gel slices

Three types of gels including tapioca starch gel, fish gel and mixed gels of both (cassava starch: fish = 1:1) were prepared under different thermal conditions. Slices (4 mm thick) derived from these the gels were dehydrated to a final moisture content of 7% in a microwave vacuum dryer. The micro/macro structure and selected quality parameters of the dried gel chips were measured e.g. shape, relative volume, bulk density, texture, color, sensory and microstructure. The measured gel characteristics were analyzed and related to structure development and selected quality attributes. Both fish and mixed gel chips expanded in both diameter and thickness while the starch gel chips shrank in diameter, but expanded in thickness; the former two represented a continuous cross-section composed of a cellular structure and expanded uniformly in thickness while the latter developed an open cross-section and the center expanded more than the edge region, indicative of a disc and pillow shape, respectively. The higher severity of thermal treatment favored greater expansion and reduced hardness and bulk density, and increased crispness in the mixed gel chips; they developed a smooth and fine surface and pore wall but decreased lightness and whiteness due to starch gelatinization in the starch and mixed gel chips. Only the partial dried mixed gel chips are acceptable to the panelists. A homogenous co-gel in the mixed gel contributed to the higher uniform expansion and cellular structure. These findings will help developing the restructured microwave vacuum-dried product by blending the starch with the fish.